The Dog's Telltale Tail (Op-Ed)

Marc Bekoff, emeritus professor at the University of Colorado, Boulder, is one of the world's pioneering cognitive ethologists, a Guggenheim Fellow, and co-founder with Jane Goodall of Ethologists for the Ethical Treatment of Animals. This essay is adapted from one that appeared in Bekoff's column Animal Emotions in Psychology Today. He contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.

Our best friends are very good at telling us what they want and how they feel. So, we assume they're also very good at telling other dogs the same things — but are they?

A dog's tail is a fascinating piece of work. Past research showed that when dogs wag their tail to the right (activation of the left side of the brain) — for example when they see their "owner" — it's an indication of a positive emotion associated with approach, and when they wag their tail to the left (right brain activation) — for example when they see an image of a dominant unfamiliar dog — it's an indication of a negative emotion associated with withdrawal. Details about this study are available in this essay called "Asymmetric tail-wagging responses by dogs to different emotive stimuli."

Brains are also fascinating pieces of work and the evolution and significance of asymmetric brains, called lateralization, is a topic worth exploring. Once thought to be a characteristic of humans alone, and one that distinguishes humans from all nonhuman animals (animals), brain lateralization refers to structural and functional differences between the left and right hemispheres of the brain. In a wide number of species, including fish, amphibians, birds and mammals, there is evidence that the left hemisphere is specialized to categorize objects and other stimuli and to take charge of routine behavior, whereas the right hemisphere is specialized to respond to novel stimuli and predators and to express intense emotions.

Research has shown that dogs react more fearfully to stimuli seen on the left and processed in the right hemisphere, and they use the right hemisphere to process disturbing sounds, such as thunder and barks of other dogs that are arousing and distressing. Dogs also use their right nostril to sniff arousing odors, which also means use of the right hemisphere since inputs from each nostril are processed by the hemisphere on the same side as the nostril (i.e. no crossing the midline as for vision).

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Concerning the dog's telltale tail, another question needing more detailed study is: What do dogs seeing a dog wag his or her tail make of the situation? Do they know that a dog wagging its tail to the right is feeling good and a dog wagging its tail to the left is feeling a negative emotion? Some of the same researchers who looked at the left and right tail-wagging have recently discovered that dogs do, in fact, draw such conclusions. A recent essay by Douglas Quenqua in the New York Times about this research called "A Dog's Tail Wag Can Say a Lot" noted, "When watching a tail wag to the left [of a silhouette of a dog projected on a screen], the dogs showed signs of anxiety, like a higher heart rate. When the tail went in the opposite direction, they remained calm."

The authors of the study concluded, "The finding that dogs are sensitive to the asymmetric tail expressions of other dogs supports the hypothesis of a link between brain asymmetry and social behavior and may prove useful to canine animal-welfare theory and practice."

So, what do the dogs really know? One of the researchers, Giorgio Vallortigara, a neuroscientist at the University of Trento in Italy, is quoted in the New York Times essay as saying, "it is unlikely that dogs are wagging their tails to communicate with one another. The mechanistic explanation is that 'It's simply a byproduct of the asymmetry of the brain,' and dogs learn to recognize the pattern over time."

Of course, the jury is still out on this conclusion and a lot of research needs to be done. However, I find the results of the second study may well indicate that dogs are indeed communicating with one another and that the various responses to different tail wags aren't so easily dismissed as being a byproduct of the asymmetry of the brain.

Some of my colleagues and I have argued that mechanistic explanations that supposedly are simpler than cognitive explanations are neither the most parsimonious nor necessarily correct. I look forward to what more research will reveal about the tales that a dog's tail tells.

In 1947, Swiss ethologist Rudolph Schenkel published an extremely important study called "Expression Studies on Wolves" in which he discussed how wolves express their emotions, including how they use their tails, and it provides interesting perspective on this latest research. Stay tuned for more on this fascinating discovery and the remarkable cognitive and emotional words of other animals.